1. Field of the Invention
The present invention relates to a stepping motor drive unit for diagnosing whether a stepping motor is rotating normally through detection of rotating conditions such as the rotating position and speed of the stepping motor, thereby correcting any error condition into a normal condition when an abnormal or error condition of the stepping motor is detected.
2. Description of the Prior Art
In recent years, there has been a rapid growth in using stepping motors both in the industrial and general consumer fields. A large number of stepping motors provided with rotation detecting means have been used for detecting error conditions such as step-out of the motors, and when abnormal or error conditions of the stepping motors are detected, the error conditions can be corrected into normal conditions.
The following describes a drive unit belonging to a conventional stepping motor having a rotation detecting function.
FIG. 12 (a) shows a block diagram of a rotation detecting unit using a potentiometer adopted as a conventional rotation detecting sensor and FIG. 12 (b) shows an example of the output of the potentiometer. The unit in FIG. 12 (a) includes a stepping motor 2, a rotor 2R for the stepping motor 2, and main coils A, A' and B, B' provided at the stator of the stepping motor 2. A potentiometer 12 is mechanically connected to the stepping motor 2 via a joint 11. The unit further includes a power source 10 and a drive circuit 9 for the stepping motor 2, both the power source 10 and the drive circuit 9 being connected to the main coils A, A' and B, B' of the stator. The potentiometer 12 has an output terminal 12' yielding an output voltage E12 which is applied to a control circuit 9' built in the drive circuit 9.
The following describes the operation of the drive unit of the conventional stepping motor using the output of the potentiometer.
In FIG. 12 (a), firstly each of the main coils A, A', B, and B' is excited according to the phase relation as shown in FIG. 2 to thereby rotate the rotor 2R of the stepping motor 2. With the rotation of the rotor 2R, the joint 11 rotates, and the output voltage E12 at the output terminal 12' of the potentiometer 12 changes according to the rotation angle of the joint 11. FIG. 12 (b) shows an example of the output voltage E12 of the potentiometer 12.
Upon detecting the output voltage E12 of the potentiometer 12 by the control circuit 9', it is judged whether the stepping motor 2 is rotating normally, with which operation any error condition can be corrected.
There has been proposed another conventional method of carrying out a rotation detecting operation by utilizing a terminal voltage of the stepping motor (which means a voltage induced between the terminal of the motor and the ground) in the same manner as the present invention. The above-mentioned conventional method employs a transformer provided outside the motor and one winding of the transformer is connected to one phase line of the main coils of the motor to utilize the voltage induced in the secondary winding of the transformer.
However, in the conventional construction mentioned above, there must be provided outside the motor a separate sensor such as a potentiometer or an external component having a comparatively large current capacity such as a transformer. Particularly when a sensor is used, a connection with the motor or a load is necessary, and the connection exerts an influence to make the sensor have a hysteresis characteristic to result in deteriorating the accuracy in position. Furthermore, the sensor problematically has a serious limitation regarding the anti-environmental property thereof. Use of an external component having a large capacity leads to no merit in cost, and furthermore a certain consideration must be taken for the inherent electric constant of the external component to result in difficulty in mass production.